text: # Copyright (c) Facebook, Inc. and its affiliates. All Rights Reserved
  """
  DETR Transformer class.
  
  Copy-paste from torch.nn.Transformer with modifications:
      * positional encodings are passed in MHattention
      * extra LN at the end of encoder is removed
      * decoder returns a stack of activations from all decoding layers
  """
  import copy
  from typing import Optional, List
  
  import torch
  import torch.nn.functional as F
  from torch import nn, Tensor
  
  from slotmachines.slotted_linear import Linear
  
  class Transformer(nn.Module):
  
      def __init__(self, d_model=512, nhead=8, num_encoder_layers=6,
                   num_decoder_layers=6, dim_feedforward=2048, dropout=0.1,
                   activation="relu", normalize_before=False,
                   return_intermediate_dec=False):
          super().__init__()
  
          encoder_layer = TransformerEncoderLayer(d_model, nhead, dim_feedforward,
                                                  dropout, activation, normalize_before)
          encoder_norm = nn.LayerNorm(d_model) if normalize_before else None
          self.encoder = TransformerEncoder(encoder_layer, num_encoder_layers, encoder_norm)
  
          decoder_layer = TransformerDecoderLayer(d_model, nhead, dim_feedforward,
                                                  dropout, activation, normalize_before)
          decoder_norm = nn.LayerNorm(d_model)
          self.decoder = TransformerDecoder(decoder_layer, num_decoder_layers, decoder_norm,
                                            return_intermediate=return_intermediate_dec)
  
          self._reset_parameters()
  
          self.d_model = d_model
          self.nhead = nhead
  
      def _reset_parameters(self):
          for p in self.parameters():
              if p.dim() > 1:
                  nn.init.xavier_uniform_(p)
  
      def forward(self, src, mask, query_embed, pos_embed):
          # flatten NxCxHxW to HWxNxC
          bs, c, h, w = src.shape
          src = src.flatten(2).permute(2, 0, 1)
          pos_embed = pos_embed.flatten(2).permute(2, 0, 1)
          query_embed = query_embed.unsqueeze(1).repeat(1, bs, 1)
          mask = mask.flatten(1)
  
          tgt = torch.zeros_like(query_embed)
          memory = self.encoder(src, src_key_padding_mask=mask, pos=pos_embed)
          hs = self.decoder(tgt, memory, memory_key_padding_mask=mask,
                            pos=pos_embed, query_pos=query_embed)
          return hs.transpose(1, 2), memory.permute(1, 2, 0).view(bs, c, h, w)
  
  
  class TransformerEncoder(nn.Module):
  
      def __init__(self, encoder_layer, num_layers, norm=None):
          super().__init__()
          self.layers = _get_clones(encoder_layer, num_layers)
          self.num_layers = num_layers
          self.norm = norm
  
      def forward(self, src,
                  mask: Optional[Tensor] = None,
                  src_key_padding_mask: Optional[Tensor] = None,
                  pos: Optional[Tensor] = None):
          output = src
  
          for layer in self.layers:
              output = layer(output, src_mask=mask,
                             src_key_padding_mask=src_key_padding_mask, pos=pos)
  
          if self.norm is not None:
              output = self.norm(output)
  
          return output
  
  
  class TransformerDecoder(nn.Module):
  
      def __init__(self, decoder_layer, num_layers, norm=None, return_intermediate=False):
          super().__init__()
          self.layers = _get_clones(decoder_layer, num_layers)
          self.num_layers = num_layers
          self.norm = norm
          self.return_intermediate = return_intermediate
  
      def forward(self, tgt, memory,
                  tgt_mask: Optional[Tensor] = None,
                  memory_mask: Optional[Tensor] = None,
                  tgt_key_padding_mask: Optional[Tensor] = None,
                  memory_key_padding_mask: Optional[Tensor] = None,
                  pos: Optional[Tensor] = None,
                  query_pos: Optional[Tensor] = None):
          output = tgt
  
          intermediate = []
  
          for layer in self.layers:
              output = layer(output, memory, tgt_mask=tgt_mask,
                             memory_mask=memory_mask,
                             tgt_key_padding_mask=tgt_key_padding_mask,
                             memory_key_padding_mask=memory_key_padding_mask,
                             pos=pos, query_pos=query_pos)
              if self.return_intermediate:
                  intermediate.append(self.norm(output))
  
          if self.norm is not None:
              output = self.norm(output)
              if self.return_intermediate:
                  intermediate.pop()
                  intermediate.append(output)
  
          if self.return_intermediate:
              return torch.stack(intermediate)
  
          return output.unsqueeze(0)
  
  
  class TransformerEncoderLayer(nn.Module):
  
      def __init__(self, d_model, nhead, dim_feedforward=2048, dropout=0.1,
                   activation="relu", normalize_before=False):
          super().__init__()
          self.self_attn = nn.MultiheadAttention(d_model, nhead, dropout=dropout)
          # Implementation of Feedforward model
          self.linear1 = Linear(d_model, dim_feedforward)
          self.dropout = nn.Dropout(dropout)
          self.linear2 = Linear(dim_feedforward, d_model)
  
          self.norm1 = nn.LayerNorm(d_model)
          self.norm2 = nn.LayerNorm(d_model)
          self.dropout1 = nn.Dropout(dropout)
          self.dropout2 = nn.Dropout(dropout)
  
          self.activation = _get_activation_fn(activation)
          self.normalize_before = normalize_before
  
      def with_pos_embed(self, tensor, pos: Optional[Tensor]):
          return tensor if pos is None else tensor + pos
  
      def forward_post(self,
                       src,
                       src_mask: Optional[Tensor] = None,
                       src_key_padding_mask: Optional[Tensor] = None,
                       pos: Optional[Tensor] = None):
          q = k = self.with_pos_embed(src, pos)
          src2 = self.self_attn(q, k, value=src, attn_mask=src_mask,
                                key_padding_mask=src_key_padding_mask)[0]
          src = src + self.dropout1(src2)
          src = self.norm1(src)
          src2 = self.linear2(self.dropout(self.activation(self.linear1(src))))
          src = src + self.dropout2(src2)
          src = self.norm2(src)
          return src
  
      def forward_pre(self, src,
                      src_mask: Optional[Tensor] = None,
                      src_key_padding_mask: Optional[Tensor] = None,
                      pos: Optional[Tensor] = None):
          src2 = self.norm1(src)
          q = k = self.with_pos_embed(src2, pos)
          src2 = self.self_attn(q, k, value=src2, attn_mask=src_mask,
                                key_padding_mask=src_key_padding_mask)[0]
          src = src + self.dropout1(src2)
          src2 = self.norm2(src)
          src2 = self.linear2(self.dropout(self.activation(self.linear1(src2))))
          src = src + self.dropout2(src2)
          return src
  
      def forward(self, src,
                  src_mask: Optional[Tensor] = None,
                  src_key_padding_mask: Optional[Tensor] = None,
                  pos: Optional[Tensor] = None):
          if self.normalize_before:
              return self.forward_pre(src, src_mask, src_key_padding_mask, pos)
          return self.forward_post(src, src_mask, src_key_padding_mask, pos)
  
  
  class TransformerDecoderLayer(nn.Module):
  
      def __init__(self, d_model, nhead, dim_feedforward=2048, dropout=0.1,
                   activation="relu", normalize_before=False):
          super().__init__()
          self.self_attn = nn.MultiheadAttention(d_model, nhead, dropout=dropout)
          self.multihead_attn = nn.MultiheadAttention(d_model, nhead, dropout=dropout)
          # Implementation of Feedforward model
          self.linear1 = Linear(d_model, dim_feedforward)
          self.dropout = nn.Dropout(dropout)
          self.linear2 = Linear(dim_feedforward, d_model)
  
          self.norm1 = nn.LayerNorm(d_model)
          self.norm2 = nn.LayerNorm(d_model)
          self.norm3 = nn.LayerNorm(d_model)
          self.dropout1 = nn.Dropout(dropout)
          self.dropout2 = nn.Dropout(dropout)
          self.dropout3 = nn.Dropout(dropout)
  
          self.activation = _get_activation_fn(activation)
          self.normalize_before = normalize_before
  
      def with_pos_embed(self, tensor, pos: Optional[Tensor]):
          return tensor if pos is None else tensor + pos
  
      def forward_post(self, tgt, memory,
                       tgt_mask: Optional[Tensor] = None,
                       memory_mask: Optional[Tensor] = None,
                       tgt_key_padding_mask: Optional[Tensor] = None,
                       memory_key_padding_mask: Optional[Tensor] = None,
                       pos: Optional[Tensor] = None,
                       query_pos: Optional[Tensor] = None):
          q = k = self.with_pos_embed(tgt, query_pos)
          tgt2 = self.self_attn(q, k, value=tgt, attn_mask=tgt_mask,
                                key_padding_mask=tgt_key_padding_mask)[0]
          tgt = tgt + self.dropout1(tgt2)
          tgt = self.norm1(tgt)
          tgt2 = self.multihead_attn(query=self.with_pos_embed(tgt, query_pos),
                                     key=self.with_pos_embed(memory, pos),
                                     value=memory, attn_mask=memory_mask,
                                     key_padding_mask=memory_key_padding_mask)[0]
          tgt = tgt + self.dropout2(tgt2)
          tgt = self.norm2(tgt)
          tgt2 = self.linear2(self.dropout(self.activation(self.linear1(tgt))))
          tgt = tgt + self.dropout3(tgt2)
          tgt = self.norm3(tgt)
          return tgt
  
      def forward_pre(self, tgt, memory,
                      tgt_mask: Optional[Tensor] = None,
                      memory_mask: Optional[Tensor] = None,
                      tgt_key_padding_mask: Optional[Tensor] = None,
                      memory_key_padding_mask: Optional[Tensor] = None,
                      pos: Optional[Tensor] = None,
                      query_pos: Optional[Tensor] = None):
          tgt2 = self.norm1(tgt)
          q = k = self.with_pos_embed(tgt2, query_pos)
          tgt2 = self.self_attn(q, k, value=tgt2, attn_mask=tgt_mask,
                                key_padding_mask=tgt_key_padding_mask)[0]
          tgt = tgt + self.dropout1(tgt2)
          tgt2 = self.norm2(tgt)
          tgt2 = self.multihead_attn(query=self.with_pos_embed(tgt2, query_pos),
                                     key=self.with_pos_embed(memory, pos),
                                     value=memory, attn_mask=memory_mask,
                                     key_padding_mask=memory_key_padding_mask)[0]
          tgt = tgt + self.dropout2(tgt2)
          tgt2 = self.norm3(tgt)
          tgt2 = self.linear2(self.dropout(self.activation(self.linear1(tgt2))))
          tgt = tgt + self.dropout3(tgt2)
          return tgt
  
      def forward(self, tgt, memory,
                  tgt_mask: Optional[Tensor] = None,
                  memory_mask: Optional[Tensor] = None,
                  tgt_key_padding_mask: Optional[Tensor] = None,
                  memory_key_padding_mask: Optional[Tensor] = None,
                  pos: Optional[Tensor] = None,
                  query_pos: Optional[Tensor] = None):
          if self.normalize_before:
              return self.forward_pre(tgt, memory, tgt_mask, memory_mask,
                                      tgt_key_padding_mask, memory_key_padding_mask, pos, query_pos)
          return self.forward_post(tgt, memory, tgt_mask, memory_mask,
                                   tgt_key_padding_mask, memory_key_padding_mask, pos, query_pos)
  
  
  def _get_clones(module, N):
      return nn.ModuleList([copy.deepcopy(module) for i in range(N)])
  
  
  def build_transformer(args):
      return Transformer(
          d_model=args.hidden_dim,
          dropout=args.dropout,
          nhead=args.nheads,
          dim_feedforward=args.dim_feedforward,
          num_encoder_layers=args.enc_layers,
          num_decoder_layers=args.dec_layers,
          normalize_before=args.pre_norm,
          return_intermediate_dec=True,
      )
  
  
  def _get_activation_fn(activation):
      """Return an activation function given a string"""
      if activation == "relu":
          return F.relu
      if activation == "gelu":
          return F.gelu
      if activation == "glu":
          return F.glu
      raise RuntimeError(F"activation should be relu/gelu, not {activation}.")
  